Spell support is now built in as of Vim 7.0. Just :set spell spelllang=en_us for example. Some people may prefer a different speller with a plugin but most users should use the built in functionality.

A little while ago, I tried out all the spelling plug-ins for Vim because I was doing a bit of a project and needed to make sure it was all beautifully spelled. One function that I found really lacking in the various spelling plug-ins was the ability to make suggestions on the current word. Some of them allowed this facility but there were restrictions, such as only being able to use it in graphical mode and only being able to use it on certain types of files. I wanted something that would work anywhere, whether in some code, in a text doc and that would work in console mode. I also wanted to see how easily I could in-line some Perl into a Vim script to perform some function on it. The answer to that was that it's not impossible, but it's a bit ugly!